1. Field of the Invention
The present invention relates to endosteal fixation of a substitute ligament and, more specifically, to arthroscopic endosteal fixation of a substitute anterior cruciate ligament using a tapered bioabsorbable interference screw.
2. Description of the Related Art
When a ligament becomes detached from a bone, surgery usually is required to reconstruct the ligament. Often, a substitute ligament or graft is secured into bone tunnels to facilitate incorporation and permanent attachment.
Various methods of graft attachment are known, including the use of interference screws to secure the graft against the walls of a tunnel drilled through the tibia and a socket formed in the femur. A strong graft attachment is obtained by using a metal interference screw to wedge a graft bone block to the wall of a graft tunnel formed through the bone, as disclosed in U.S. Pat. No. 5,211,647 to Schmieding. If a bioabsorbable interference screw is used, the graft is often wedged directly against the bone by the screw, without a bone block.
Bioabsorbable interference screws are usually sized so that they are slightly larger that the diameter of the tunnel, so that they dilate the bone tunnel upon insertion. Dilation advantageously compacts the soft cancellous bone between the ends of the tunnel, providing better fixation. Conventional straight-sided bioabsorbable interference screws have an interference fit of about 1 mm., i.e, about 1 mm. of bone is dilated as the screw is inserted into the bone tunnel. Although it would be desirable to use larger diameter screws for increased fixation strength, larger screws have larger tips and are more difficult to align and insert correctly. Accordingly, a need exists for a bioabsorbable interference screw which provides increased dilation and interference fit without increased difficulty of insertion.